The invention relates to screens in printing machines in general, and more particularly to improvements in screen printing machines with reciprocable screens. Still more particularly, the invention relates to improvements in screen printing machines of the type wherein a screen is reciprocable at one side of the path for a web or sheet of material to be treated opposite a sheet- or web-supporting cylinder.
German Offenlegungsschrift No. 2 332 534 of Brasa discloses a printing machine wherein a flat screen is reciprocable in a horizontal plane at a level above the path for an intermittently transported web of paper or the like and opposite a rotary web-supporting cylinder. The latter further serves as a means for intermittently advancing the web along its path. A drawback of the screen printing machine of Brasa is that its space requirements are excessive, especially if the machine comprises two or more screen printing units each with a horizontal screen which is reciprocable in its plane between a foremost and a rearmost position. Each screen reciprocates relative to a discrete stationary cylinder. Since the machine of Brasa is designed for multicolor screen printing, it must comprise at least two discrete screens and an equal number of cylinders. The screens cannot be placed close to each other because there must remain ample room for reciprocatory movements of screens in and counter to the direction of advancement of the web through successive screen printing units.
U.S. Pat. No. 3,252,411 to Black discloses a screen printing machine which applies ink, adhesive or other coating materials to intermittently advance paper sheets. The space requirements of the machine of Black are just as unsatisfactory as those of the machine of Brasa because the machine of Black also employs one or more flat screens which must reciprocate in horizontal planes. As a rule, the space requirements of each screen printing unit correspond to twice the length of its reciprocable horizontal screen. Furthermore, neighboring screen printing units are normally separated by drying means which also occupy substantial amounts of space.
German Pat. No. 23 26 371 to Dubuit discloses a machine which is used to apply printed matter to or to otherwise coat bottles, tubes, pipes or other hollow objects which are rotatably mounted on mandrels indexible by a disc along an endless path and past two successive screen printing units employing mutually inclined screens. The machine of Dubuit is not suitable for screen printing of continuous webs or sheets of paper or the like. Moreover, the space requirements of the machine of Dubuit are enormous because the disc carries a complete annulus of mandrels which are to support a large number of hollow objects. Still further, the versatility of the patented machine is unsatisfactory because the two screens are invariably compelled to move in synchronism.
Austrian Pat. No. 192373 to Hediger discloses a screen printing machine with an inclined screen which is pivotable about a fixed horizontal axis.
Japanese patent application Ser. No. 55-184544 of Kagai discloses an ink applicator for use in a screen printing machine. The applicator employs a first pump which delivers ink to a screen adjacent a doctor and draws non-applied ink from a reservoir adjacent a second pump. The screen printing machine of Kagai operates with a horizontal screen.
Further screen printing machines with horizontal screens are disclosed in commonly owned German Offenlegungsschrift No. 31 36 175 and in commonly owned U.S. Pat. Nos. 4,510,864, 4,589,336 and 4,628,814.
Apparatus for drying webs in a screen printing machine are disclosed in commonly owned U.S. Pat. Nos. 4,619,050 and 4,628,620, and commonly owned U.S. Pat. No. 4,249,688 discloses a device for intermittent feeding of webs in screen printing machines.
A drawback which is common to all screen printing machines known to applicant at this time, especially to those screen printing machines wherein the web is transported from a supply reel to a takeup reel, is that it is not possible to readily monitor the quality of freshly applied printed matter. This is particularly disadvantageous in multicolor printing machines. The reciprocating horizontal screens or stationary horizontal screens of such machines obstruct the actual printing station or stations so that it is possible to monitor only the quality of those increments of a running web which leave the single screen printing unit or the last screen printing unit of the machine. This often necessitates discarding of considerable lengths of treated material because of improper application (absence of accurate register) of different types of printing media on top of or next to each other and/or because the application of one or more coats of printing media to certain portions of the web is less satisfactory than to others.